ASSESSMENT OF THE SIZE AND STRUCTURE OF

ASSESSMENT OF THE SIZE AND STRUCTURE OF

Teka Kom. Ochr. Kszt. Środ. Przyr. – OL PAN, 2008, 5, 181–189
ASSESSMENT OF THE SIZE AND STRUCTURE
OF LAKE MINNOW Eupallasella percnurus (Pallas, 1814)
POPULATION INHABITING A SMALL WATER BODY
IN CENTRAL POLAND
Jacek Wolnicki*, Rafał Kamiński*, Justyna Sikorska*, Jan Kusznierz**
*Pond Fishery Department in Żabieniec, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn
Żabieniec, 05–500 Piaseczno, [email protected]
**Zoological Institute, Wrocław University, Sienkiewicza str. 21, 50–335 Wrocław
Summary. The present study was the first attempt at evaluating the size and sex structure of the
population of lake minnow Eupallasella percnurus, a critically endangered in Poland cyprinid fish
species, by means of the capture-recapture Lincoln-Petersen method. The study area was a small
(approx. 0.1 ha) man-made fire reservoir located near town of Zielonka in the Mazowieckie
Voivodeship. To assess the age structure of the population, frequency distribution of fish total
length was used. The total size of the population was estimated at 2000–2500 individuals, including males, females and juveniles aged 1+ or older. Male-to-female ratio in mature individuals was
found to be 1 : 2. Young fish belonging to 1+ and 2+ age classes dominated in the population,
which may indicate that it is overcrowded. The capture-recapture method appears to be useful in
the spawning period for the evaluation of the size and structure of E. percnurus population,
provided that fish behaviour – considerably influencing fish recapture rates – is taken into consideration.
Key words: lake minnow, population size, sex structure, length distribution, age structure
INTRODUCTION
The lake minnow Eupallasella percnurus is a tiny cyprinid fish of vast geographical range in the northern hemisphere, extending from the territory of Poland in
the west to the Pacific Ocean in the east. This species belongs to the most endangered
representatives of the Polish freshwater ichthyofauna [Witkowski 1999]. It is law-protected and included in the Polish Red Data Book of Animals [Kusznierz 2001]. This
fish is also a priority vertebrate species in the European Ecological Natura 2000 Network [Kusznierz et al. 2005]. The Polish populations inhabit small water bodies, at
present man-made rather than natural ones, most often strongly shallowed remnants of
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Jacek Wolnicki et al.
old peat excavations. Such water bodies are highly liable to total destruction resulting
particularly from water deficits [Wolnicki et al. 2008a, b].
Conservation of E. percnurus requires protection of both its habitats and the
most valuable populations within the Special Protection Areas (SPAs), included in the
Natura 2000 Network [Kusznierz et al. 2005]. To this end, reliable data on the condition of the particular populations are indispensable. However, because of the almost
complete lack of related scientific studies in the recent past and presently, knowledge
of all the Polish populations of this species remains far out of date and superficial.
The present work was devoted to assessing the size and basic structure of
E. percnurus population inhabiting a small water body situated in Central Poland.
This E. percnurus station will presumably be involved in the Natura 2000 Network.
STUDY AREA
The study area was a midforest isolated water body (52°17’46” N, 21°08’29”
E), named Zielonka, located at a close distance from the town of Zielonka in the
Mazowieckie Voivodeship in Central Poland. This water body came into existence in the 1960s as a fire reservoir, but E. percnurus was found to occur there
only in the spring of 2006 [Wolnicki et al. 2006a, 2008b].
Fig. 1. Location of traps used for the 1st and the 2nd catch of E. percnurus in Zielonka
The water surface of 0.07–0.12 ha and the maximum water depth of 0.5–1.5
m, dependent mainly on precipitation, proved to be highly variable both
throughout a year and from year to year [Wolnicki et al. 2008b and unpubl.
data]. By today about 90% of the bottom of the water body has become extremely shallowed. As a consequence, this part of the bottom is densely overgrown with the common reed Phragmites australis (Fig. 1). Larger water depth
has been retained in two small parts of the water body. Bigger and deeper one was
ASSESSMENT OF THE SIZE AND STRUCTURE OF LAKE MINNOW...
183
used as a catching area.
MATERIAL AND METHODS
In the present study, the following parameters of E. percnurus population
were assessed: size, sex structure and fish length distribution. The last parameter
was then used to evaluate the age structure of the population [Bagenal and Tesch
1978]. The fish abundance was estimated using the capture-recapture (mark-recapture) Lincoln-Petersen method [Skórka et al. 2003]. The method is considered reliable for so-called closed populations, in which neither immigration
nor emigration occurs [Seber 1982, Williams et al. 2002]. The station in
Zielonka is an entirely isolated water body and is not subject to any stronger
angling pressure, therefore E. percnurus living there perfectly complied with the
precondition of being an isolated population.
The 1st fish catch was conducted on June 5, 2008, whereas the 2 nd one (fish
recapture) took place 4 days later, i.e. in the middle of E. percnurus spawning
period [Wolnicki 2005]. Water temperature was then about 16°C. Fishing was
performed with the use of specialized folding traps with two openings
(25 × 25 × 40 cm; mesh 5 mm; opening diameter 60 mm), with a piece of bread
used as bait [Wolnicki et al. 2006b, 2007]. Traps were placed in the deepest part
of the water body, free from emerged macrophytes (Fig. 1), with the depth while
fish catching of 0.5–0.9 m. Eight and five traps were used in the 1st and 2nd catch,
respectively, and the exposition time was 1–2 hours.
Prior to any manipulation, captured fish were anaesthetized in water solution of 2-phenoxyethanol at 0.45 g dm-3 [Kamiński et al. 2004]. Three fish
groups, i.e. mature males, mature females and juvenile individuals of indeterminable sex were distinguished. Larval E. percnurus (age 0+) were not found
among fish trapped. To determine fish sex, both their primary and secondary
sexual characteristics were taken into account. Males were identified after gentle
pressing their belly when profuse milt was released by the point of protruding
sex papilla. Moreover, indistinct spawning rash was present on male head, and
their fins were coloured bright orange. Female fish had more or less rounded
belly with no sex papilla, and their sexual opening was enlarged and reddened.
Some females released eggs spontaneously. Individuals showing no distinct
male or female morphological features were considered as juveniles. All males,
females and juveniles, captured in the 1st catch, were counted. Before being set
free, all of them were marked by clipping the end part (2–3 mm long) of their
right pelvic fin. From among them, fish belonging to three distinguished groups
were randomly taken to measure their total length to the nearest 0.1 mm (total
n = 205). In the 2nd catch, the number of marked and not marked males, females
and juveniles was determined.
Jacek Wolnicki et al.
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RESULTS
All fish trapped were E. percnurus individuals. In the 1st catch, vast majority of fish were those recorded in traps placed in the southern zone of the catching area. A total of 621 fish were captured then, among them 184 mature males
and 288 mature females (Tab. 1). In the 2nd catch, 367 fish were captured, including 75 males and 227 females; marked were 13 males and 90 females. The
recapture rates for both these fish groups equalled to 7.1 and 31.3%, respectively. The juvenile individuals were recaptured at the rate of 9.4%. Using separate data related to all fish groups, the total number of E. percnurus individuals in
the population was estimated at 2480 fish. This figure included 1062 mature
male individuals and 726 mature females.
Table 1. Number of E. percnurus individuals captured in Zielonka, recapture rates and estimated
size of the population
Number
of marked
fish
(M)
184
288
149
Fish groups
Mature males
Mature females
Juveniles
Total
621
Number of fish
in the 2nd catch
Total
Marked
(C)
(R)
75
13
227
90
65
14
367
117
Number of fish
in a population
(N)**
Recapture rate*
(%)
7.1
31.3
9.4
–
1062 (857–1393)
726 (674–787)
692 (565–892)
2480 (2097–3072)
*Recapture rate = R ⋅ M ⋅ 100; ** N = M ⋅ C ⋅ R ; in brackets 95% confidence limit.
-1
-1
The sex structure of E. percnurus population is shown in Table 2. Calculations
were done for all captured individuals or for mature fish only. The share of male
and female fish in the whole population was estimated at 26.2 and 52.1%, respectively. When juvenile fish were excluded from the calculations, the respective
figures equalled 33.5 and 66.5%, respectively. In both cases male-to-female ratio
was nearly 1 : 2.
Table 2. Sex structure of E. percnurus population in Zielonka
Fish groups
Mature males
Mature females
Juveniles
Juveniles included
(%)
26.2
52.1
21.7
Juveniles excluded
(%)
33.5
66.5
–
Percentages computed using the pooled direct results of the 1st and 2nd catch.
ASSESSMENT OF THE SIZE AND STRUCTURE OF LAKE MINNOW...
185
The mean total length of juvenile, male and female E. percnurus individuals was 48.2, 62.0 and 70.4 mm, respectively, and all these values differed significantly (P ≤ 0.05, Student’s t-test). The fish total length distribution in the population is illustrated, separately for juveniles, males and females, in Figure 2.
Fig. 2. Total length distribution in E. percnurus population in Zielonka
The population was dominated by individuals belonging to two age classes: 1+
and 2+, and the few largest females probably represented the 3+ age class. Among fish
aged 1+, numerous males and some females attained sexual maturity.
DISCUSSION
The present study is the only known attempt to assess – using capture-recapture
Lincoln-Petersen method – the size and structure of E. percnurus population in Poland. It should be stressed that no results of similar studies with this fish species and
the same catching method can be found in any published sources of information. The
fundamental question then arises about the appropriateness of the method used in the
present work to evaluate E. percnurus populations.
It can be seen from our results that in the total number of fish, captured in the 1 st
and 2nd catch, a substantial difference took place (621 v. 367 individuals, respectively;
Tab. 1). Furthermore, considerable differences were found between both these catches
as concerns the percentage share of individuals belonging to all distinguished fish
groups, i.e. mature males, mature females and juveniles. For example, 288 females
captured in the 1st catch constitute 46.4% of the total number of fish caught then. For
the 2nd catch, the respective value is much higher – 61.9%. Also noteworthy is the fact
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that considerable differences were recorded concerning the recapture rates for all fish
groups, ranging from 31.3% for females to only 7.1% for males.
As to the differences in the total number of the captured fish, one of possible explanations of this phenomenon could be the fact that different number of traps was
used in the 1st and 2nd catch (8 v. 5, respectively). Although, in the first case, vast majority of fish were those captured closely to the southern shore of the water body (that
is why lower number of traps was used in the 2nd catch), it seems likely that applying 8
traps also in the 2nd catch would have then resulted in higher total number of the captured fish and higher recapture rates of marked individuals.
All these explanations, however, do not elucidate the reasons for the remaining
two phenomena mentioned above. It should be emphasized that the present study was
carried out in E. percnurus spawning period. This was because distinct morphological
differences, existing only at that time, made it possible to infallibly distinguish males,
females and older juveniles [Wolnicki 2005]. Therefore, it can be assumed that the
fishing results, obtained in the present study, remained under the influence of fish
spawning behaviour, being not necessarily identical for both catches as well as for all
fish groups. Hence, females might have been attracted by the bait stronger and swam
into traps more eagerly as compared to male or juvenile individuals. Consequently, female fish distinctly dominated in both catches and attained relatively high recapture
rate. In contrast, recorded for both males and juveniles, considerably lower recapture
rates may be not representative for the actual share of these groups in E. percnurus
population as a whole.
It seems difficult at present to decide about the real reasons for the aforementioned findings. However, it should be mentioned here that in very similar field study
of E. percnurus population, occurring in Kowalicha (another small water body in the
Mazowieckie Voivideship), the recapture rates, recorded for male, female and
juvenile fish, were considerably higher and very uniform, ranging just from 40
to 50% [Wolnicki et al. 2008a and unpubl. data].
If then the recapture rates recorded for males and juveniles in Zielonka are really
not representative, the use of separate data for the three fish groups can lead to overestimation of the actual population size. On the other hand, the use of pooled data may
cause its underestimation [e.g. Beukema and de Vos 1974]. As a matter of fact, the
latter approach is commonly practised in studies of fish populations [Beukema and de
Vos 1974, Piironen and Holopainen 1988, Brönmark et al. 1995]. In the case of the
population from Zielonka, the recalculated figure concerning the total fish number –
based on the pooled data from Table 1 – would equal to 1948 individuals (95% confidence limit of 1819–2096 individuals).
Taking into account all the doubts mentioned above, the male-to-female ratio for
the population under study can be estimated to be 1 : 2 (Tab. 2). This fact should not
be considered surprising. More or less pronounced domination of adult female individuals over adult males in E. percnurus populations, both in the Siberian and Polish
water bodies, is well documented [e.g. Kaj 1953, Brusynina 1974, Kusznierz unpubl.
ASSESSMENT OF THE SIZE AND STRUCTURE OF LAKE MINNOW...
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data]. It is interesting that this regularity was proven with the use of different fishing
methods, including angling.
The distribution of E. percnurus total length indicates clearly that the discussed
population consisted of young individuals, mostly at the age of 1+ or 2+, whereas only
the few largest females might belong to the 3+ class (Fig. 2). Of importance is the fact
that some of the smallest fish, especially males, proved to reach sexual maturity. Both
lack of age classes over 3+ and early maturation of E. percnurus individuals are good
indicators of overcrowded populations, inhabiting very small and shallow water bodies [Zukov 1965, Movchan 1976, Tandon 1979, Movchan and Smirnov 1981,
Kusznierz unpubl data].
CONCLUSION
As evidenced by the results of the present work, the capture-recapture Lincoln-Petersen method, with the use of specialized traps, can be successfully applied to evaluate the size and basic structure of E. percnurus populations inhabiting small water bodies. However, it should be taken into consideration that in
the spawning period the results obtained for different groups of individuals (mature males, mature females, immature individuals) may not be representative due
to different fish behaviour.
REFERENCES
Bagenal T.B., Tesch F.W., 1978. Age and growth [in:] T.B. Bagenal (ed.) Methods for the assessment of fish production in fresh waters. Blackwell Scientific Publications, Oxford, 101–136.
Beukema J. J., de Vos G.J., 1974. Experimental tests of a basic assumption of the capture-recapture
method in pond populations of carp Cyprinus carpio L. J. Fish. Biol., 6, 317–329.
Brönmark C., Paszkowski C.A., Tonn W.M., Hargeby A., 1995. Predation as a determinant of size
structure in populations of crucian carp (Carassius carassius) and tench (Tinca tinca). Ecol.
Freshwat. Fish, 4, 85–92.
Brusynina I.N., 1974. Growth and size structure of lake minnow population (in Russian). Academy
of Sciences of the SSSR, Ural Research Centre, Tomsk, 146–149.
Kaj J., 1953. Distribution and breed variability of fish from the species Phoxinus percnurus Pall.
in Poland. Pol. Arch. Hydrobiol., 1, 49–78.
Kamiński R., Kusznierz J., Myszkowski L., Wolnicki J., 2004. The first attempt to artificially reproduce the endangered cyprinid lake minnow Eupallasella perenurus (Pallas). Aquacult. Int., 12,
3–10.
Kusznierz J., 2001. Eupallasella percnurus (Pallas, 1811). Lake (swamp) minnow (in Polish) [in:] Głowaciński Z. (ed.) Polish Red Data Book of Animals. Vertebrates. PWRiL, Warszawa, pp. 301–303.
Kusznierz J., Wolnicki J., Radtke G., 2005. Swamp-minnow Eupallasella perenurus (Pallas) – status
and perspectives of protection (in Polish). Chrońmy Przyrodę Ojczystą, 61, 70–78.
188
Jacek Wolnicki et al.
Movchan Yu.V., 1976. Morphoecological characteristics of lake minnow Phoxinus percnurus (Pallas) – (Pisces, Cyprinidae) in some water bodies in Ukraine (in Russian). Zoological Museum,
Academy of Sciences of the USSR, 36, 54–62.
Movchan Yu.V., Smirnov A.I., 1981. Fauna of Ukraine. Fishes. Cyprinid fishes (in Ukrainian).
Naukova Dumka, Kiev.
Piironen J., Holopainen I.J., 1988. Length structure and reproductive potential of crucian carp
(Carassisus carassius (L.)) populations in some small forest ponds. Ann. Zool. Fennici, 25, 203–208.
Seber G.A.F., 1982. The estimation of animal abundance and related parameters. 2nd Ed. Blackburn
Press, Caldwell, New Jersey.
Skórka P., Nowicki P., Witek M., 2003. Population size estimation with capture-mark-recapture
methods – standards and new solutions (in Polish). Wiad. Ekol., 49, 205–220.
Tandon K.K., 1979. Age and growth of Phoxinus percnurus (Pallas, 1811) from Poland. Zool. Pol.,
27, 187–194.
Williams B.K., Nichols J.D., Conroy M.J., 2002. Analysis and management of animal populations.
Academic Press, San Diego, California.
Witkowski A., 1992. Threats and protection of freshwater fishes in Poland. Neth. J. Zool., 2–3, 243–259.
Wolnicki J., 2005. The lake minnow Eupallasella perenurus (Pallas, 1814) (in Polish) [in:]
Adamski P., Bartel R., Bereszyński A., Kepel A., Witkowski Z. (eds) Animals species (except
for birds). Guide of habitats and species protection. Nature 2000. Warszawa,t. 6, 229–233.
Wolnicki J., Kamiński R., Sikorska J., 2006a. Actual state of the occurrence of lake minnow in the
Mazowieckie Voivodeship (in Polish). Komun. Ryb., 4, 25–28.
Wolnicki J., Kolejko M., Sikorska J., 2006b. Present state of the occurrence of lake minnow Eupallasella perenurus (Pallas, 1814) in the Lubelskie Voivodeship (Poland). Teka Kom. Ochr.
Kszt. Środ. Przyr., 3, 250–256.
Wolnicki J., Sikorska J., Kolejko M., Kamiński R., Radtke G., 2007. Newest discoveries of lake minnow Eupallasella percnurus (Pallas, 1814) stations in Poland. Teka Kom. Ochr. Kszt. Środ.
Przyr., 4, 314–321.
Wolnicki J., Kamiński R., Sikorska J., 2008a. Conservation of the imperilled cyprinid fish species,
lake minnow (Eupallasella percnurus), in Poland. Europ. Aquacult. Soc. Spec. Publ., 37, 696–697.
Wolnicki J., Sikorska J., Kamiński R., 2008b. Occurrence and conservation of the endangered cyprinid fish species, lake minnow Eupallasella percnurus (Pallas, 1814) in the Mazowieckie
Voivodeship in Poland. Teka Kom. Ochr. Kszt. Środ. Przyr., 5, (in press).
Zukov P.I., 1965. Fishes of Belarus (in Russian). Nauka i Technika, Minsk.
OCENA WIELKOŚCI I STRUKTURY POPULACJI STRZEBLI BŁOTNEJ
Eupallasella percnurus (Pallas, 1814) ZAMIESZKUJĄCEJ
MAŁY ZBIORNIK WODNY W ŚRODKOWEJ POLSCE
Streszczenie. Niniejsza praca jest pierwszą próbą określenia liczebności oraz struktury krajowej populacji
strzebli błotnej Eupallasella percnurus z zastosowaniem metody znakowania i połowu Lincolna-Petersena. Przedmiotem badań była populacja z przeciwpożarowego zbiornika wodnego (52°17’46” N,
21°08’29” E), znajdującego się koło miasta Zielonka. W czerwcu 2008 r. za pomocą pułapek z przynętą złowiono łącznie 621 osobników strzebli błotnej. Oznaczono płeć złowionych ryb lub – w przypadku niemożności jej ustalenia – zakwalifikowano do grupy osobników młodocianych. Wszyst-
ASSESSMENT OF THE SIZE AND STRUCTURE OF LAKE MINNOW...
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kie ryby oznakowano przez obcięcie końcowego fragmentu (2–3 mm) prawej płetwy brzusznej. U
losowo wybranych z każdej grupy osobników (łącznie n = 205) zmierzono długość całkowitą, a
następnie wszystkie ryby uwolniono do macierzystego zbiornika. Po czterech dniach przeprowadzono ponowny połów. Tym razem złowiono 367 osobników, w tym 117 znakowanych. W drugim połowie udział osobników znakowanych wynosił od 31,3 (samice) do 7,1% (samce). Na podstawie danych na temat liczby osobników znakowanych wykazano, że liczebność populacji obliczona metodą standardową (tj. dla wszystkich ryb łącznie) była mniejsza (n = 1948) niż liczebność
obliczona przez zsumowanie liczebności wyróżnionych grup ryb (n = 2480). Różnica ta wskazuje
na różne prawdopodobieństwo złowienia osobników z poszczególnych grup, co może mieć podłoże behawioralne, wynikające z trwającego tarła. W takim przypadku niski procent złowionych
znakowanych samców i osobników młodocianych mógłby oznaczać niepełną reprezentatywność
tych danych. Użycie do oszacowania całkowitej liczebności populacji danych dla wszystkich grup
ryb oddzielnie może prowadzić do jej przeszacowania, a użycie tych danych łącznie – do niedoszacowania. Stosunek liczebności dojrzałych samców i samic w populacji oszacowano na podstawie bezpośrednich wyników obu połowów na 1 : 2. Analiza struktury długości całkowitej złowionych ryb wykazała, że w populacji dominują osobniki młode w wieku 1+ oraz 2+, z których część,
głównie samce, osiągnęła dojrzałość płciową. Taka struktura wiekowa jest charakterystyczna dla
przegęszczonych populacji strzebli błotnej, bytujących w bardzo małych i płytkich zbiornikach
wodnych.
Słowa kluczowe: strzebla błotna, liczebność populacji, struktura płciowa, rozkład długości, struktura wiekowa
This study was in part supported by the S-001 Project of the Inland Fisheries Institute in Olsztyn.